This section provides background information related to the present disclosure which is not necessarily prior art.
One common type of uninterruptible power supply (UPS) system is a double conversion UPS system that has a rectifier that converts AC input power to DC power that is provided via a DC bus to an inverter that converts the DC power back to AC power. A circuit breaker is coupled between an AC power input and an input of the rectifier. The AC power input is coupled to a source of AC power, such as a power feed from a utility. An LC input circuit is coupled between an AC input of the rectifier and the circuit breaker and a fuse is typically coupled between the circuit breaker and the LC circuit. In this regard, if the UPS system is a three-phase system, the rectifier has three AC inputs and the circuit breaker has three poles and a respective LC input circuit is coupled between each pole of the circuit breaker and a respective one of the AC inputs of the rectifier. One type of double conversion UPS system does not have an input transformer coupled between the AC input of the rectifier and the AC power input and is referred to herein as a transformer-less rectifier UPS system. It should be understood that such transformer-less rectifier UPS system can have a transformer coupled between an output of the inverter and an output of the UPS system or not have a transformer coupled between the output of the inverter and the output of the UPS system.
In transformer-less rectifier UPS systems, when the circuit breaker is closed, large inrush currents flow from the source of the AC power to the capacitors of the LC input circuits. This typically requires additional considerations and design costs for the circuit/fuse design to address the effects of these large inrush currents.